using System;

namespace Chaos.NaCl.Internal.Ed25519Ref10;

internal static partial class ScalarOperations
{
    private static Int64 load_3(byte[] input, int offset)
    {
        Int64 result;
        result = (Int64)input[offset + 0];
        result |= ((Int64)input[offset + 1]) << 8;
        result |= ((Int64)input[offset + 2]) << 16;
        return result;
    }

    private static Int64 load_4(byte[] input, int offset)
    {
        Int64 result;
        result = (Int64)input[offset + 0];
        result |= ((Int64)input[offset + 1]) << 8;
        result |= ((Int64)input[offset + 2]) << 16;
        result |= ((Int64)input[offset + 3]) << 24;
        return result;
    }

    /*
    Input:
      a[0]+256*a[1]+...+256^31*a[31] = a
      b[0]+256*b[1]+...+256^31*b[31] = b
      c[0]+256*c[1]+...+256^31*c[31] = c

    Output:
      s[0]+256*s[1]+...+256^31*s[31] = (ab+c) mod l
      where l = 2^252 + 27742317777372353535851937790883648493.
    */

    public static void sc_muladd(byte[] s, byte[] a, byte[] b, byte[] c)
    {
        Int64 a0 = 2097151 & load_3(a, 0);
        Int64 a1 = 2097151 & (load_4(a, 2) >> 5);
        Int64 a2 = 2097151 & (load_3(a, 5) >> 2);
        Int64 a3 = 2097151 & (load_4(a, 7) >> 7);
        Int64 a4 = 2097151 & (load_4(a, 10) >> 4);
        Int64 a5 = 2097151 & (load_3(a, 13) >> 1);
        Int64 a6 = 2097151 & (load_4(a, 15) >> 6);
        Int64 a7 = 2097151 & (load_3(a, 18) >> 3);
        Int64 a8 = 2097151 & load_3(a, 21);
        Int64 a9 = 2097151 & (load_4(a, 23) >> 5);
        Int64 a10 = 2097151 & (load_3(a, 26) >> 2);
        Int64 a11 = (load_4(a, 28) >> 7);
        Int64 b0 = 2097151 & load_3(b, 0);
        Int64 b1 = 2097151 & (load_4(b, 2) >> 5);
        Int64 b2 = 2097151 & (load_3(b, 5) >> 2);
        Int64 b3 = 2097151 & (load_4(b, 7) >> 7);
        Int64 b4 = 2097151 & (load_4(b, 10) >> 4);
        Int64 b5 = 2097151 & (load_3(b, 13) >> 1);
        Int64 b6 = 2097151 & (load_4(b, 15) >> 6);
        Int64 b7 = 2097151 & (load_3(b, 18) >> 3);
        Int64 b8 = 2097151 & load_3(b, 21);
        Int64 b9 = 2097151 & (load_4(b, 23) >> 5);
        Int64 b10 = 2097151 & (load_3(b, 26) >> 2);
        Int64 b11 = (load_4(b, 28) >> 7);
        Int64 c0 = 2097151 & load_3(c, 0);
        Int64 c1 = 2097151 & (load_4(c, 2) >> 5);
        Int64 c2 = 2097151 & (load_3(c, 5) >> 2);
        Int64 c3 = 2097151 & (load_4(c, 7) >> 7);
        Int64 c4 = 2097151 & (load_4(c, 10) >> 4);
        Int64 c5 = 2097151 & (load_3(c, 13) >> 1);
        Int64 c6 = 2097151 & (load_4(c, 15) >> 6);
        Int64 c7 = 2097151 & (load_3(c, 18) >> 3);
        Int64 c8 = 2097151 & load_3(c, 21);
        Int64 c9 = 2097151 & (load_4(c, 23) >> 5);
        Int64 c10 = 2097151 & (load_3(c, 26) >> 2);
        Int64 c11 = (load_4(c, 28) >> 7);
        Int64 s0;
        Int64 s1;
        Int64 s2;
        Int64 s3;
        Int64 s4;
        Int64 s5;
        Int64 s6;
        Int64 s7;
        Int64 s8;
        Int64 s9;
        Int64 s10;
        Int64 s11;
        Int64 s12;
        Int64 s13;
        Int64 s14;
        Int64 s15;
        Int64 s16;
        Int64 s17;
        Int64 s18;
        Int64 s19;
        Int64 s20;
        Int64 s21;
        Int64 s22;
        Int64 s23;
        Int64 carry0;
        Int64 carry1;
        Int64 carry2;
        Int64 carry3;
        Int64 carry4;
        Int64 carry5;
        Int64 carry6;
        Int64 carry7;
        Int64 carry8;
        Int64 carry9;
        Int64 carry10;
        Int64 carry11;
        Int64 carry12;
        Int64 carry13;
        Int64 carry14;
        Int64 carry15;
        Int64 carry16;
        Int64 carry17;
        Int64 carry18;
        Int64 carry19;
        Int64 carry20;
        Int64 carry21;
        Int64 carry22;

        s0 = c0 + a0 * b0;
        s1 = c1 + a0 * b1 + a1 * b0;
        s2 = c2 + a0 * b2 + a1 * b1 + a2 * b0;
        s3 = c3 + a0 * b3 + a1 * b2 + a2 * b1 + a3 * b0;
        s4 = c4 + a0 * b4 + a1 * b3 + a2 * b2 + a3 * b1 + a4 * b0;
        s5 = c5 + a0 * b5 + a1 * b4 + a2 * b3 + a3 * b2 + a4 * b1 + a5 * b0;
        s6 = c6 + a0 * b6 + a1 * b5 + a2 * b4 + a3 * b3 + a4 * b2 + a5 * b1 + a6 * b0;
        s7 = c7 + a0 * b7 + a1 * b6 + a2 * b5 + a3 * b4 + a4 * b3 + a5 * b2 + a6 * b1 + a7 * b0;
        s8 = c8 + a0 * b8 + a1 * b7 + a2 * b6 + a3 * b5 + a4 * b4 + a5 * b3 + a6 * b2 + a7 * b1 + a8 * b0;
        s9 = c9 + a0 * b9 + a1 * b8 + a2 * b7 + a3 * b6 + a4 * b5 + a5 * b4 + a6 * b3 + a7 * b2 + a8 * b1 + a9 * b0;
        s10 = c10 + a0 * b10 + a1 * b9 + a2 * b8 + a3 * b7 + a4 * b6 + a5 * b5 + a6 * b4 + a7 * b3 + a8 * b2 + a9 * b1 + a10 * b0;
        s11 = c11 + a0 * b11 + a1 * b10 + a2 * b9 + a3 * b8 + a4 * b7 + a5 * b6 + a6 * b5 + a7 * b4 + a8 * b3 + a9 * b2 + a10 * b1 + a11 * b0;
        s12 = a1 * b11 + a2 * b10 + a3 * b9 + a4 * b8 + a5 * b7 + a6 * b6 + a7 * b5 + a8 * b4 + a9 * b3 + a10 * b2 + a11 * b1;
        s13 = a2 * b11 + a3 * b10 + a4 * b9 + a5 * b8 + a6 * b7 + a7 * b6 + a8 * b5 + a9 * b4 + a10 * b3 + a11 * b2;
        s14 = a3 * b11 + a4 * b10 + a5 * b9 + a6 * b8 + a7 * b7 + a8 * b6 + a9 * b5 + a10 * b4 + a11 * b3;
        s15 = a4 * b11 + a5 * b10 + a6 * b9 + a7 * b8 + a8 * b7 + a9 * b6 + a10 * b5 + a11 * b4;
        s16 = a5 * b11 + a6 * b10 + a7 * b9 + a8 * b8 + a9 * b7 + a10 * b6 + a11 * b5;
        s17 = a6 * b11 + a7 * b10 + a8 * b9 + a9 * b8 + a10 * b7 + a11 * b6;
        s18 = a7 * b11 + a8 * b10 + a9 * b9 + a10 * b8 + a11 * b7;
        s19 = a8 * b11 + a9 * b10 + a10 * b9 + a11 * b8;
        s20 = a9 * b11 + a10 * b10 + a11 * b9;
        s21 = a10 * b11 + a11 * b10;
        s22 = a11 * b11;
        s23 = 0;

        carry0 = (s0 + (1 << 20)) >> 21; s1 += carry0; s0 -= carry0 << 21;
        carry2 = (s2 + (1 << 20)) >> 21; s3 += carry2; s2 -= carry2 << 21;
        carry4 = (s4 + (1 << 20)) >> 21; s5 += carry4; s4 -= carry4 << 21;
        carry6 = (s6 + (1 << 20)) >> 21; s7 += carry6; s6 -= carry6 << 21;
        carry8 = (s8 + (1 << 20)) >> 21; s9 += carry8; s8 -= carry8 << 21;
        carry10 = (s10 + (1 << 20)) >> 21; s11 += carry10; s10 -= carry10 << 21;
        carry12 = (s12 + (1 << 20)) >> 21; s13 += carry12; s12 -= carry12 << 21;
        carry14 = (s14 + (1 << 20)) >> 21; s15 += carry14; s14 -= carry14 << 21;
        carry16 = (s16 + (1 << 20)) >> 21; s17 += carry16; s16 -= carry16 << 21;
        carry18 = (s18 + (1 << 20)) >> 21; s19 += carry18; s18 -= carry18 << 21;
        carry20 = (s20 + (1 << 20)) >> 21; s21 += carry20; s20 -= carry20 << 21;
        carry22 = (s22 + (1 << 20)) >> 21; s23 += carry22; s22 -= carry22 << 21;

        carry1 = (s1 + (1 << 20)) >> 21; s2 += carry1; s1 -= carry1 << 21;
        carry3 = (s3 + (1 << 20)) >> 21; s4 += carry3; s3 -= carry3 << 21;
        carry5 = (s5 + (1 << 20)) >> 21; s6 += carry5; s5 -= carry5 << 21;
        carry7 = (s7 + (1 << 20)) >> 21; s8 += carry7; s7 -= carry7 << 21;
        carry9 = (s9 + (1 << 20)) >> 21; s10 += carry9; s9 -= carry9 << 21;
        carry11 = (s11 + (1 << 20)) >> 21; s12 += carry11; s11 -= carry11 << 21;
        carry13 = (s13 + (1 << 20)) >> 21; s14 += carry13; s13 -= carry13 << 21;
        carry15 = (s15 + (1 << 20)) >> 21; s16 += carry15; s15 -= carry15 << 21;
        carry17 = (s17 + (1 << 20)) >> 21; s18 += carry17; s17 -= carry17 << 21;
        carry19 = (s19 + (1 << 20)) >> 21; s20 += carry19; s19 -= carry19 << 21;
        carry21 = (s21 + (1 << 20)) >> 21; s22 += carry21; s21 -= carry21 << 21;

        s11 += s23 * 666643;
        s12 += s23 * 470296;
        s13 += s23 * 654183;
        s14 -= s23 * 997805;
        s15 += s23 * 136657;
        s16 -= s23 * 683901;
        s23 = 0;

        s10 += s22 * 666643;
        s11 += s22 * 470296;
        s12 += s22 * 654183;
        s13 -= s22 * 997805;
        s14 += s22 * 136657;
        s15 -= s22 * 683901;
        s22 = 0;

        s9 += s21 * 666643;
        s10 += s21 * 470296;
        s11 += s21 * 654183;
        s12 -= s21 * 997805;
        s13 += s21 * 136657;
        s14 -= s21 * 683901;
        s21 = 0;

        s8 += s20 * 666643;
        s9 += s20 * 470296;
        s10 += s20 * 654183;
        s11 -= s20 * 997805;
        s12 += s20 * 136657;
        s13 -= s20 * 683901;
        s20 = 0;

        s7 += s19 * 666643;
        s8 += s19 * 470296;
        s9 += s19 * 654183;
        s10 -= s19 * 997805;
        s11 += s19 * 136657;
        s12 -= s19 * 683901;
        s19 = 0;

        s6 += s18 * 666643;
        s7 += s18 * 470296;
        s8 += s18 * 654183;
        s9 -= s18 * 997805;
        s10 += s18 * 136657;
        s11 -= s18 * 683901;
        s18 = 0;

        carry6 = (s6 + (1 << 20)) >> 21; s7 += carry6; s6 -= carry6 << 21;
        carry8 = (s8 + (1 << 20)) >> 21; s9 += carry8; s8 -= carry8 << 21;
        carry10 = (s10 + (1 << 20)) >> 21; s11 += carry10; s10 -= carry10 << 21;
        carry12 = (s12 + (1 << 20)) >> 21; s13 += carry12; s12 -= carry12 << 21;
        carry14 = (s14 + (1 << 20)) >> 21; s15 += carry14; s14 -= carry14 << 21;
        carry16 = (s16 + (1 << 20)) >> 21; s17 += carry16; s16 -= carry16 << 21;

        carry7 = (s7 + (1 << 20)) >> 21; s8 += carry7; s7 -= carry7 << 21;
        carry9 = (s9 + (1 << 20)) >> 21; s10 += carry9; s9 -= carry9 << 21;
        carry11 = (s11 + (1 << 20)) >> 21; s12 += carry11; s11 -= carry11 << 21;
        carry13 = (s13 + (1 << 20)) >> 21; s14 += carry13; s13 -= carry13 << 21;
        carry15 = (s15 + (1 << 20)) >> 21; s16 += carry15; s15 -= carry15 << 21;

        s5 += s17 * 666643;
        s6 += s17 * 470296;
        s7 += s17 * 654183;
        s8 -= s17 * 997805;
        s9 += s17 * 136657;
        s10 -= s17 * 683901;
        s17 = 0;

        s4 += s16 * 666643;
        s5 += s16 * 470296;
        s6 += s16 * 654183;
        s7 -= s16 * 997805;
        s8 += s16 * 136657;
        s9 -= s16 * 683901;
        s16 = 0;

        s3 += s15 * 666643;
        s4 += s15 * 470296;
        s5 += s15 * 654183;
        s6 -= s15 * 997805;
        s7 += s15 * 136657;
        s8 -= s15 * 683901;
        s15 = 0;

        s2 += s14 * 666643;
        s3 += s14 * 470296;
        s4 += s14 * 654183;
        s5 -= s14 * 997805;
        s6 += s14 * 136657;
        s7 -= s14 * 683901;
        s14 = 0;

        s1 += s13 * 666643;
        s2 += s13 * 470296;
        s3 += s13 * 654183;
        s4 -= s13 * 997805;
        s5 += s13 * 136657;
        s6 -= s13 * 683901;
        s13 = 0;

        s0 += s12 * 666643;
        s1 += s12 * 470296;
        s2 += s12 * 654183;
        s3 -= s12 * 997805;
        s4 += s12 * 136657;
        s5 -= s12 * 683901;
        s12 = 0;

        carry0 = (s0 + (1 << 20)) >> 21; s1 += carry0; s0 -= carry0 << 21;
        carry2 = (s2 + (1 << 20)) >> 21; s3 += carry2; s2 -= carry2 << 21;
        carry4 = (s4 + (1 << 20)) >> 21; s5 += carry4; s4 -= carry4 << 21;
        carry6 = (s6 + (1 << 20)) >> 21; s7 += carry6; s6 -= carry6 << 21;
        carry8 = (s8 + (1 << 20)) >> 21; s9 += carry8; s8 -= carry8 << 21;
        carry10 = (s10 + (1 << 20)) >> 21; s11 += carry10; s10 -= carry10 << 21;

        carry1 = (s1 + (1 << 20)) >> 21; s2 += carry1; s1 -= carry1 << 21;
        carry3 = (s3 + (1 << 20)) >> 21; s4 += carry3; s3 -= carry3 << 21;
        carry5 = (s5 + (1 << 20)) >> 21; s6 += carry5; s5 -= carry5 << 21;
        carry7 = (s7 + (1 << 20)) >> 21; s8 += carry7; s7 -= carry7 << 21;
        carry9 = (s9 + (1 << 20)) >> 21; s10 += carry9; s9 -= carry9 << 21;
        carry11 = (s11 + (1 << 20)) >> 21; s12 += carry11; s11 -= carry11 << 21;

        s0 += s12 * 666643;
        s1 += s12 * 470296;
        s2 += s12 * 654183;
        s3 -= s12 * 997805;
        s4 += s12 * 136657;
        s5 -= s12 * 683901;
        s12 = 0;

        carry0 = s0 >> 21; s1 += carry0; s0 -= carry0 << 21;
        carry1 = s1 >> 21; s2 += carry1; s1 -= carry1 << 21;
        carry2 = s2 >> 21; s3 += carry2; s2 -= carry2 << 21;
        carry3 = s3 >> 21; s4 += carry3; s3 -= carry3 << 21;
        carry4 = s4 >> 21; s5 += carry4; s4 -= carry4 << 21;
        carry5 = s5 >> 21; s6 += carry5; s5 -= carry5 << 21;
        carry6 = s6 >> 21; s7 += carry6; s6 -= carry6 << 21;
        carry7 = s7 >> 21; s8 += carry7; s7 -= carry7 << 21;
        carry8 = s8 >> 21; s9 += carry8; s8 -= carry8 << 21;
        carry9 = s9 >> 21; s10 += carry9; s9 -= carry9 << 21;
        carry10 = s10 >> 21; s11 += carry10; s10 -= carry10 << 21;
        carry11 = s11 >> 21; s12 += carry11; s11 -= carry11 << 21;

        s0 += s12 * 666643;
        s1 += s12 * 470296;
        s2 += s12 * 654183;
        s3 -= s12 * 997805;
        s4 += s12 * 136657;
        s5 -= s12 * 683901;
        s12 = 0;

        carry0 = s0 >> 21; s1 += carry0; s0 -= carry0 << 21;
        carry1 = s1 >> 21; s2 += carry1; s1 -= carry1 << 21;
        carry2 = s2 >> 21; s3 += carry2; s2 -= carry2 << 21;
        carry3 = s3 >> 21; s4 += carry3; s3 -= carry3 << 21;
        carry4 = s4 >> 21; s5 += carry4; s4 -= carry4 << 21;
        carry5 = s5 >> 21; s6 += carry5; s5 -= carry5 << 21;
        carry6 = s6 >> 21; s7 += carry6; s6 -= carry6 << 21;
        carry7 = s7 >> 21; s8 += carry7; s7 -= carry7 << 21;
        carry8 = s8 >> 21; s9 += carry8; s8 -= carry8 << 21;
        carry9 = s9 >> 21; s10 += carry9; s9 -= carry9 << 21;
        carry10 = s10 >> 21; s11 += carry10; s10 -= carry10 << 21;

        unchecked
        {
            s[0] = (byte)(s0 >> 0);
            s[1] = (byte)(s0 >> 8);
            s[2] = (byte)((s0 >> 16) | (s1 << 5));
            s[3] = (byte)(s1 >> 3);
            s[4] = (byte)(s1 >> 11);
            s[5] = (byte)((s1 >> 19) | (s2 << 2));
            s[6] = (byte)(s2 >> 6);
            s[7] = (byte)((s2 >> 14) | (s3 << 7));
            s[8] = (byte)(s3 >> 1);
            s[9] = (byte)(s3 >> 9);
            s[10] = (byte)((s3 >> 17) | (s4 << 4));
            s[11] = (byte)(s4 >> 4);
            s[12] = (byte)(s4 >> 12);
            s[13] = (byte)((s4 >> 20) | (s5 << 1));
            s[14] = (byte)(s5 >> 7);
            s[15] = (byte)((s5 >> 15) | (s6 << 6));
            s[16] = (byte)(s6 >> 2);
            s[17] = (byte)(s6 >> 10);
            s[18] = (byte)((s6 >> 18) | (s7 << 3));
            s[19] = (byte)(s7 >> 5);
            s[20] = (byte)(s7 >> 13);
            s[21] = (byte)(s8 >> 0);
            s[22] = (byte)(s8 >> 8);
            s[23] = (byte)((s8 >> 16) | (s9 << 5));
            s[24] = (byte)(s9 >> 3);
            s[25] = (byte)(s9 >> 11);
            s[26] = (byte)((s9 >> 19) | (s10 << 2));
            s[27] = (byte)(s10 >> 6);
            s[28] = (byte)((s10 >> 14) | (s11 << 7));
            s[29] = (byte)(s11 >> 1);
            s[30] = (byte)(s11 >> 9);
            s[31] = (byte)(s11 >> 17);
        }
    }
}